late 14c., thecchen, from Old English þeccan "to cover, cover over, conceal," in late Old English specifically "cover the roof of a house," related to þæc "roof, thatching material," from Proto-Germanic *thakan (cognates: Old Saxon thekkian, Old Norse þekja, Old Frisian thekka, Middle Dutch decken, Dutch dekken, Old High German decchen, German decken "to cover"), from PIE *(s)teg- (2) "to cover" (see stegosaurus).

Old English þæc "roof, thatch, cover of a building," from the source of thatch (v.). Compare Old Norse þak, Old Frisian thek, Swedish tak, Danish tag, Middle Dutch, Dutch dak "roof," Old High German dah "covering, cover," German Dach "roof."